Document: NIC-3-59-104

Carbon pulse-chase into soil biota: An in situ stable isotope approach.

OSTLE, N.* ¹, P.INESON ² and A.FITTER ²

Centre for Ecology and Hydrology Grange-Over-Sands, Cumbria, LA11 6JU, United Kingdom ¹
University of York, York, YO10 5YW, United Kingdom ²

Abstract:
The link between biological diversity and ecosystem function remains poorly understood. We hypothesised that biogeochemical cycling of fundamental elements such as carbon (C) would be altered by changes in soil biodiversity. The effects of changes in soil biodversity on C fluxes through the soil-plant system were measured in a typical upland pasture. A mobile Stable Isotope Delivery laboratory (SID) was used to supply a tracer 'pulse' in situ. Studies and experiments made in 1999 and 2000 involved isotopic labelling of upland vegetation and soil biota with 50% atom ¹³CO₂ at atmospheric concentrations (approximately 350 ppm) using flow rates of up to 5 L min-1. Automated online sampling and analyses enabled the determination of plant CO₂ assimilation, soil CO₂ respiration and headspace ^13/12CO₂ ratios. Using this technique, ¹³C derived from pulse labelled swards was traced into soil biota, organic matter and individual molecules allowing quantification of ¹³C incorporation and turnover in selected C pools. Results from in situ investigations showed that 70-80% of photosynthate C was lost from the plant biomass within 24 hours of assimilation. This loss was followed into a cascade of trophic groups of soil biota enabling Collembola, Acari, Enchytraeid worms and earthworms to be separated into classes according to photosynthate C incorporation and turnover.

Keywords: ¹³C , CO₂, soil, biodiversity, mesofauna, grassland, C dynamics

This abstract is being presented at: 11:15 AM in session:
Oral Session #71: Soil Microbial Biomass and Soil Respiration.